1. Field of the Invention
The present invention relates generally to the field of dopant compositions and methods for producing high concentration phosphoro-silica dopants on a semiconductor device.
2. Prior Art
The fabrication of alloyed semiconductor devices is extremely well known in the semiconductor art. The problems raised by the prior art techniques and which have not been solved relate to the creation of an abundant source of phosphorus so as to allow deep diffusion in the semiconductor devices for doping purposes. In the prior art, there was no effective way to do the N+ drive especially in Hexa-mesa rectifiers. This was thought to be due to the fact that the N+ drive generally employs pyrolytic decomposition depositions.
Before describing the present invention, and in terms of the background of this area of endeavor, a brief discussion of the formation of any semiconductor device will be set forth. Semiconductors have been used for many years. The term "semiconductor device" as used herein, is used in its generic sense to include a number of materials such as the well known silicon-type semiconductor. Generally, such semiconductor devices are in the form of a wafer or disc of varying shapes. Silicon is one preferrable semiconductor material in that it is characterized by having a relatively wide gap at the top of its valence band and the bottom of its conduction band. This property of silicon makes possible stable electron operation at relatively high temperature and also results in low currents across a P-N junction region.
As is well recognized in the semiconductor art, a region of semiconductor material containing an excess of donor impurities and yielding an excess of free electrons, is considered to be an impurity doped N-type region. An impurity doped P-type region is one containing an excess of acceptor impurities resulting in a deficiency of electrons or an excess of holes. Therefore, an N-type material is one characterized by electron conduction whereas a P-type material is one characterized by a hole concentration. As used herein, and as well recognized in the art, when a semiconductor device has N-type region adjacent to a P-type region, the boundary between them is termed a P-N or N-P junction.
The present invention is concerned with a P- or N-type semiconductor device in which a N-type region is formed by a phosphorus containing layer. In the past, semiconductor devices containing a diffused P-N junction have been made by heating P-type silicon chips or wafers in the presence of a phosphorus compound such as phosphorus pentoxide. The phosphorus pentoxide is believed to form a glassy film over the surface of the wafer and subsequently, with continued heating, elemental phosphorus diffuses into the silicon. The prior art also discloses methods in which the phosphorus is deposited on the surface of the silicon wafer at low temperature and then heated to a temperature at which diffusion will take place.
While various developments have taken place in the prior art to effect the doping of semiconductor material by addition of dopant impurities, they all suffer from various shortcomings. One specific shortcoming is the fact that the diffusion of the phosphorus into the semiconductor device is generally very shallow. One such method involving deposition of a dopant is described in U.S. Pat. No. 3,287,187. The method disclosed therein requires the deposition of an oxide of the semiconductor material by vapor deposition followed by diffusion of the doping substance into the semiconductor surface by heating the semiconductor body. Yet another method of diffusing phosphorus into a semiconductor device is described in U.S. Pat. No. 3,998,668. In that patent, the source of phosphorus is provided by high purity aluminum metaphosphate. The aluminum metaphosphate functions as a source for the controlled release of phosphorus pentoxide vapors which are directed to the desired face of the silicon wafer. The method therefore requires the heating of the aluminum metaphosphate so as to produce the phosphorus pentoxide vapors. After the vapors react with a heated silicon surface, elemental phosphorus diffuses into the silicon chip with continued heating. Other related patents discussing various methods of providing a semiconductor with a phosphorus-containing composition include U.S. Pat. Nos. 3,607,467; 3,697,334; 3,510,369; and 2,974,073. As discussed hereinabove each of those above identified patents contains significant shortcomings in the manner in which the phosphorus composition is applied to the semiconductor device. The present invention contains none of the above identified shortcomings and provides a composition which can be used to provide an abundant source of phosphorus so as to permit deep diffusion in a semiconductor device.